Electrically conductive organic polymers have been of scientific and technological interest since the late 1970's. These relatively new materials exhibit the electronic and magnetic properties characteristic of metals while retaining the physical and mechanical properties associated with conventional organic polymers. Herein we describe electrically conducting polymers, for example polyparaphenylene vinylenes, polyparaphenylenes, polyanilines, polythiophenes, polyazines, polyfuranes, polypyrroles, polyselenophenes, poly-p-phenylene sulfides, polythianapthenes, polyacetylenes formed from soluble precursors, combinations thereof and blends thereof with other polymers and copolymers of the monomers thereof.
These polymers are conjugated systems which are made electrically conducting by doping. The non-doped or non-conducting form of the polymer is referred to herein as the precursor to the electrically conducting polymer. The doped or conducting form of the polymer is referred to herein as the conducting polymer.
Conducting polymers have potential for a large number of applications in such areas as electrostatic charge/discharge (ESC/ESD) protection, electromagnetic interference (EMI) shielding, resists, electroplating, corrosion protection of metals and ultimately metal replacements, i.e. wiring, plastic microcircuits, conducting pastes for various interconnection technologies (solder alternative) etc.. Many of the above applications especially those requiring high current capacity have not yet been realized because the conductivity of the processable conducting polymers is not yet adequate for such applications. In order for these materials to be used in place of metals in more applications, it is desirable to increase the conductivity of these materials. In addition, the processability of these polymers also requires improvement. Although some of these polymers are soluble, the solubility is generally limited and the solutions tend to be not stable over time.
The polyaniline class of conducting polymers has been shown to be one of the most promising and most suited conducting polymers for a broad range of commercial applications. The polymer has excellent environmental stability and offers a simple, one-step synthesis. However, the conductivity of the material in its most general form (unsubstituted polyaniline doped with hydrochloric acid) is generally on the low end of the metallic regime most typically, on the order of 1 to 10 S/cm (A. G. Macdiarmid and A. J. Epstein, Faraday Discuss. Chem. Soc. 88, 317, 1989). In addition, the processability of this class of polymers requires improvement. Although polyaniline is a soluble polymer, it has been noted that the solutions tend to be unstable with time. (E. J. OH et al, Synth. Met. 55-57, 977 (1993). Solutions of for example the polyaniline in the non-doped form tend to gel upon standing. Solutions greater than 5% solids concentration tend to gel within hours limiting the applicability of the polymer. It is desirable to devise methods of increasing the electrical conductivity of the doped polyanilines and to enhance the processability of these systems to allow broader applicability.
The conductivity (.sigma.) is dependent on the number of carriers (n) set by the doping level, the charge on the carriers (q) and on the mobility (g) (both interchain and intrachain mobility) of the carriers. EQU .sigma.=n q .mu.
Generally, n (the number of carriers) in these systems is maximized and thus, the conductivity is dependent on the mobility of the carriers. To achieve higher conductivity, the mobility in these systems needs to be increased. The mobility, in turn, depends on the morphology of the polymer. The intrachain mobility depends on the degree of conjugation along the chain, presence of defects, and on the chain conformation. The interchain mobility depends on the interchain interactions, the interchain distance, and the degree of crystallinity. Thus, the conductivity is very dependent on the morphology of the polymer.
Recently, it has been shown that polyaniline in the non-doped form has a tendency to aggregate as a result of interchain hydrogen bonding and that this aggregation limits the solvation of the polymer (U.S. application Ser. No. 08/370,127 filed on Jan. 9, 1995 and U.S. application Ser. No. 08/370,128 filed on Jan. 9, 1995, the teachings of which are incorporated herein by reference). It was found that certain additives such as lithium chloride could be added to the polyaniline to disrupt the aggregation. As the aggregation was disrupted, the chains became disentangled from each other and the solvent was able to more effectively solvate the chains to adapt a more expanded chain conformation. As a result, the deaggregated polymer upon doping exhibited higher levels of conductivity than did the polymer in the aggregated form. In addition, it was found that the deaggregated solutions were more stable with time than the corresponding aggregated solutions.
Herein novel methods of deaggregating conducting polymers are described which involve oxidation and reduction reactions.